Black lines through every part after importing GLTF
Those are empties (what you get from doing Add &gt; Empty &gt; Plain Axes in the 3D Viewport). They are created for glTF nodes that have no mesh, no camera, aren't a bone, etc.
You can try running this script from the Text Editor to hopefully clean up some of them that aren't necessary. Save beforehand.
import bpy
while True:
    dead = [ob for ob in bpy.data.objects if ob.data is None and not ob.children]
    if not dead: break
    for ob in dead:
        bpy.data.objects.remove(ob, do_unlink=True)